1. Field of the Invention
This invention relates to a vibration-type angular-velocity detector. The detector is mountable on a vehicle, such as a four wheel drive vehicle and is utilized as a yaw-rate detection mechanism in a vehicle posture control system or a navigation system.
2. Description of the Related Art
To control posture of a vehicle, angular-velocity information of the vehicle, such as the yaw-rate, must be detected. Sensor mechanisms for detecting angular-velocity are typically mounted on a vehicle.
A vibration-type angular-velocity sensor has been used for detecting the angular-velocity of a vehicle. A tuning-fork type sensor, such as shown in FIG. 5 of the accompanying drawings, or a tuning-fork type vibrating body, shown in FIG. 6, has been used for this purpose.
In the angular velocity sensor shown in FIG. 5, driving piezoelectric devices 52 are bonded to opposed surfaces of a vibration body 51. The vibration body 51 is shaped into a rectangular cube. Detection piezoelectric devices 53 are bonded to the other opposed surfaces of the vibration body 51. The vibrating body 51 vibrates when an A.C. driving signal is applied to the driving piezoelectric devices 52. The angular velocity of the vibration body 51 is detected by the detection piezoelectric devices 53.
The tuning-fork type angular-velocity sensor, shown in FIG. 6, comprises a tuning-fork type driving body 55 including a pair of leg plates 551 and 552. Driving piezoelectric devices 56 are bonded to the leg plates 551 and 552, respectively. Detection plates 571 and 572 are integrally connected to the distal ends of the leg plates 551 and 552, respectively, in such a manner as to cross, at right angles, the vibration planes of the leg plates 551 and 552. Detection piezoelectric devices 581 and 582 are bonded to the plane surfaces of the detection plates 571 and 572, respectively.
Both of the tuning fork type angular-velocity sensors, having the construction described above and shown in FIGS. 5 and 6, are used such that the longitudinal direction (Z axis) of the vibration bodies 51 and 55 are is aligned with the axis of the angular velocity. Accordingly, when the angular velocity sensor is mounted on a vehicle so as to detect a yaw-rate, for example, the height of the sensor mechanism cannot be reduced.
An electronic control system, such as a posture control system or a navigation system, must detect the yaw-rate of the vehicle. Therefore, it is necessary to assemble the angular-velocity detection mechanism into the electronic control system. However, the angular velocity sensor, having the construction shown in FIG. 5 or 6, cannot be easily assembled into the electronic control system because of the the relatively large height of the vibration body.
Other types of angular-velocity detection mechanisms and means for reducing the size of the overall construction may be conceivable. However, in order to obtain a suitable detection performance, the relative accuracy of the vibrating body must be sufficiently improved and its size reduced, without increasing production costs.